We propose to undertake an investigation of the detailed effects of fluorine substitution on the electronic structures, chemical properties and carcinogenic activities of four typical polycyclic aromatic carcinogens: benzo(a)pyrene, dibenzo(a,i)pyrene, dibenzo(a,h)pyrene, and 5-methylchrysene. This will be done experimentally, using NMR spectroscopy to define the effects of fluorine on bond localization, electron densities and rates and sites of deuteriodeprotonation; and theoretically using self-consistent field molecular orbital calculations. We will investigate the stability of C-F bonds in polycyclic carcinogens in vitro. Compounds will also be tested for carcinogenic activity. Our biological and deuteriodeprotonation data for fluorinated dibenzo(a,i)-pyrene suggest that fluorine can exert long-range deactivating effects across the entire molecule, in addition to its direct blocking effect on metabolic transformations. Thus, this study will constitute a critical evaluation of the fluorine substitution methodology for identifying sites of metabolic transformation. The data will also allow an experimental test of the bay-region hypothesis of carcinogenicity.